Think OP intends to list parking areas for a stay longer than load/unload time.

FCO used to be a godsend in the past. Airport authorities as a result restricted day by day lots available.
Anyway there's still a fair amount of free chances, esp. if you avoid holiday season and move on for an early morning flight.

Also for NAP exist slight chances of success for cars, much higher for moto, just in front the arrivals, in designated areas.